Human umbilical cord blood cells (HUCBC) are well known specific immunomodutators that confer a balanced (i.e. without complete immunosuppression, GVHD, or rejection) alteration of both peripheral and central immune responses. Other investigators have demonstrated they promote mobilization of adult bone marrow (BM) progenitor cells. In addition we recently demonstrated sera derived from HUCBC-infused PSAPP mice significantly inhibited microglial CD40 expression induced by IFN-? and markedly increased microglial A phagocytic activity without unacceptable immune compromise. In confirmation, this effect was inhibited by the ligation of CD40 with CD40L protein. Importantly, primary adult microglia from these HUCBC-infused mice also showed increased A phagocytic activity, and a strong A IgG titer. Together these data suggest a balanced alteration of both innate and humoral immune microenvironments mediated by an HUCBC induced suppression of CD40 signaling and enhancement of A IgG production. In accord with this downregulation of neurotoxic innate responses and upregulation of salutary humoral responses, A levels/- amyloid deposits and cerebral amyloid angiopathy (CAA; an inflammatory response to vascular amyloid deposits) are reduced by HUCBC infusion in vivo, with attendant: (a) increased serum levels of A1-40, 42, suggesting efflux from the CNS (b) decreased soluble CD40L serum levels, (c) decreased microglial CD40 expression, and finally, (d) elevated CNS/serum levels of anti-inflammatory (IL-10 and TGF-21) with decrease pro-inflammatory cytokines (IL-1 and TNF-a). Finally, our preliminary data suggests that, compared with control primary BM derived monocytes/macrophages (MO/X), MO/X from HUCBC-infused PSAPP mice show enhanced A phagocytic activity. These data along with our previous findings that crossing Tg2576 mice with CD40L null mice or treating PSAPP mice with CD40L antibody reduced A loads, lead us to hypothesize that HUCBC infusion confers a mitigation of A/-amyloid pathology in Alzheimer's disease (AD) mice by alterations in innate and humoral immunity mediated by CD40-CD40L disruption resulting in mobilization of BM-derived progenitor MO/X, increased anti-inflammatory cytokine production, and increased amyloid clearance from the brain. Here we propose to test the hypothesis that HUCBC mediated dampening of the CD40-CD40L interaction reduces amyloidosis by investigating CD40 signaling in HUCBC infused PSAPP mice. Based on our preliminary data, we additionally plan to reconstitute the effects of HUCBC infusion by administering IL- 10, TGF-1 and NGF- alone and in combinations; key factors we found to be essential for HUCBC ability to modulate CD40 activity and amyloidosis without systemic immunosuppression, rejection, or GVHD. Also, we will test the hypothesis that HUCBC infusion mobilizes BM-derived MO/X, leading to transdifferentiation into macrophages which enter the CNS and further differentiate into microglia with enhanced A phagocytic capacity. It is our long-term goal to move this combination treatment into phase I human trials for patients with mild to moderate AD.